Weird Ocean Current May Create Coral Refuges

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Global warming is expected to have devastating effects on coral
reefs, but recent research points to a few exceptions.

Warming in the equatorial Pacific may actually create refuges for
corals around a handful of islands, even as it bleaches, or
kills, corals elsewhere, suggests new research that predicts
increased upwelling of cold, nutrient-rich water in these places.

"These little islands in the middle of the ocean
can counteract global trends and have a big impact on their
own future, which I think is a beautiful concept," said study
researcher Kristopher Karnauskas, a Woods Hole Oceanographic
Institution scientist, in a press release issued by the
institution.

If predictions made by Karnauskas and colleague Anne Cohen are
accurate, warming around the Gilbert Islands will be slower than
elsewhere, giving the corals and their symbiotic algae a better
chance to adapt. Perhaps these refuges could eventually become a
source of new corals and other species that could recolonize
reefs damaged by warming, Karnauskas said.

Corals are animals that host tiny plants, or algae, that feed
them using photosynthesis. The reefs corals build provide
important habitat for many species. Warming water can cause
corals to expel their algae, a
phenomenon called bleaching, which turns the corals white and
puts them under great stress and at risk of death.

Global climate models predict the central tropical Pacific will
warm by about 5.0 degrees Fahrenheit (2.8 degrees Celsius) by the
end of the century. To get a better idea of how conditions might
play out on a small geographic scale, the researchers used the
global models in combination with a fine-scale regional model.

The low-lying coral atoll islands, part of
the nation of Kiribati, are as small as 1.54 square miles (4
square kilometers).

As a result of other changes caused
by warming, their work predicts the deep equatorial
undercurrent (EUC), an eastward flowing current at the equator,
will strengthen by 14 percent; this strengthening would create
habitat for corals to flourish alongside the islands by bringing
cooler water and nutrients to the surface. Though the EUC is an
east-to-west current, when it hits an island, water gets
deflected upward.

"Our model suggests that the amount of upwelling will actually
increase by about 50 percent around these islands and reduce the
rate of warming waters around them by about 1.25 degrees F (0.7
degrees C) per century," Karnauskas said.

The research appears in the April 30 issue of the journal Nature
Climate Change.